Tests: cleanup script a bit
dsolve: improve a bit, add tests, still needs work
python_cmd: reset the ipc mechanism if python raised error

Allows user to continue working after an error.

OctSymPy is not stateful: so this just spams stdout a bit and then
minor slowdown for next command.  In IPC system() it is overkill, but
harmless.

Fixes #79.  But I'm sure our error handling could still be improved.
allow empty syms other than 0x0

Fixes #124.
horizcat/vertcat: allow concatenation with 0x0 empties

Fixes #123.  Should give errors wuth nx0 or 0xm in somes cases
but does not.  Left xtest FIXME.
same symbol diff asdumptions makes two outputs in sym, findsymbols

Improve docs, tests
symfun: improve symvar

symvar skould prefer the explicit vars of the symfun, at least
for `symvar(f, n)` form.  `symvar(f)` still gives alphabetical
order.

Some discrepancy with SMT here: what to do when symfun does not
depend on its vars?  Left fixme and xtest for this.
drop shared vars in horz/vertcat

mainly to test formating of "FAIL 1" in octsympy_tests
octsympy_tests: did not display the "FAIL 1" text

do not subtract the xfails to determine nfail
octsympy_tests: time the tests
add isvector, octave dev version now needs this
NEWS: add isvector to list of new functions
vertcat: simplify a test, split off failing as xtest...
Merge pull request #130 from cbm755/dev

various changes, fixes